A torque fluctuation absorber is arranged on a power transmission path between an engine and a transmission, and absorbs (restricts) fluctuating torque generated between the engine and the transmission. The torque fluctuation absorber may include a damper portion for absorbing the fluctuating torque by means of an elastic force (a spring force). The damper portion includes two rotating members, and an elastic member (a coil spring) arranged between the two rotating members in a circumferential direction thereof so that the coil spring absorbs the fluctuating torque by contracting in a case where the two rotating members rotate relative to each other.
A device provided with the aforementioned damper portion may be structured in a manner that one of the rotating members is arranged at an outer periphery and/or at both sides of the other one of the rotating members, and a clearance between one of the rotating members and the other one of the rotating members is closed by means of a seal member. Thus, a space in which the coil spring is accommodated is sealed. The device provided with the aforementioned damper portion may be structured in a manner that one of the rotating members is rotatably supported at the other one of the rotating members via a bearing.
For example, according to EP0960292B1 (hereinafter referred to as Patent reference 1), a clearance between a damper plate and a cover is closed by means of a sealing joint fixed to the damper plate, and thus a space in which an elastic member is accommodated is sealed. In addition, according to Patent reference 1, a clearance between a mass and a flange is closed by means of a bearing, and thus the space in which the elastic member is accommodated is sealed.
According to U.S. Pat. No. 6,620,048 B2 (hereinafter referred to as Patent reference 2), a clearance between a side wall and an inner section is closed by means of an annular seal fixed to the side wall, and thus a chamber is sealed. A flywheel fixed to the inner section is rotatably supported via a ball bearing at a hub fixed to the side wall.
According to JP2007-218346A (hereinafter referred to as Patent reference 3), a space in which a damper member is accommodated is covered with a flywheel and with a cover member, and thus the space is sealed.
However, in a case where the space into which ingress of muddy water needs to be restricted (that is, the space in which the coil spring is accommodated) is sealed to be an air tightly-sealed closed space as is found in known torque fluctuation absorbers, a pressure difference between an internal gas (most thereof is air) and atmospheric air between an operation time and a down time may be caused by a temperature change of the internal gas. The pressure difference acts at a seal portion, at which rigidity is relatively low.
In a case where the seal portion does not resist the pressure difference, there may be the following drawbacks. When the internal pressure is negative, muddy water in a vicinity of the seal portion may possibly come into an inside of the air tightly-sealed closed space, and when the internal pressure is positive, for example, grease enclosed in the space and existing in a vicinity of the seal portion may possibly leak out to an outside of the space.
In addition, a specification is set so that the seal portion resists the pressure difference when the seal portion is new, however, the seal portion made of elastic material (rubber or resin material) may not maintain an initial configuration thereof due to creep and/or stress relaxation because a deformation caused by a pressing force is further added to a normal interference at the seal portion as the temperature increases/decreases. In other words, the seal portion incurs permanent deformation and may possibly not ensure a sealing performance.
In order to resolve the aforementioned drawbacks, adjustment of the interference of the seal portion may be considered. In a case where the interference of the seal portion is decreased, the robustness of the sealing performance (that is, a capability to restrict changes in the sealing performance) decreases. On the other hand, in a case where the interference of the seal portion is increased, hysteresis of damping characteristics increases and a damping performance decreases. In other words, according to the sealing structure of the known torque fluctuation absorbers, even in a case where the interference of the seal portion is adjusted, it is difficult to ensure the sealing performance and the damping performance due to the aforementioned tradeoff.
A need thus exists for a torque fluctuation absorber which is not susceptible to the drawback mentioned above.